Apparatus for melting highly reactive metals



May 15, 1956 P. F. DARBY ETAL 2,745,891

APPARATUS FOR MELTING HIGHLY REACTIVE METALS Filed March 15, 1954 3 Sheets-Sheet l EN TORS (/1- F. DARBY. ALTEeLJ /A/LAK Y Oe/EN WS/MMOMS'.

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May 15, 1956 P. F. DARBY ETAL 2,745,891

APPARATUS FOR MELTING HIGHLY REACTIVE METALS Filed March 15, 1954 3 Sheets-Sheet 2 25 P420 121 gm K INVENTORS. PA UL I: DA ear.

n ALTEE L. FI'NLAK BY OlP/EN WS/MMONS.

ATTUAIVEVJI May 15, 1956 p, DARBY ETAL APPARATUS FOR MELTING HIGHLY REACTIVE METALS 3 Sheets-Sheet 5 Filed March 15, 1954 INV NT F3401. FDAR K ORS Vl/A TERLHNL BY O? ATTORNEYS.

United States Patent 0 APPARATUS FOR MELTING HIGHLY REAQJTIVE METALS Paul F. Darby, Walter L. Finlay, and Orion W. fiimnrons, Beaver, Pa., assignors to Rem-Cm Titanium, lnm, Wildland, Pa., a corporation of Pennsylvania Application March 15, 1954, Serial No. 416,063 16 Claims. (Cl. 13-31) This invention pertains to improved apparatus for the melting and casting of refractory metals which are highly reactive in the molten state, such as titanium and zirconium and alloys of each.

This application is an improvement of the invention disclosed in the copending application of Milton B. Vordahl and Walter L. Finlay Serial No. 357,704, filed May 27, 1953.

In the following disclosure of the present invention titanium will be used as an illustrative example, although it will be understood that the same remarks apply with equal force to other refractory metals which are highly reactive chemically when molten, such as those mentioned as well as others of an equivalent nature.

As has been pointed out in the above said copending application, titanium melts at a temperature of about 1725 C., i. e., about 3140 F., and, in the molten state is so highly reactive that it attacks and destroys all such high temperature refractories as alumina, zirconium, thoria and graphite. In contact with refractory metallic oxides, it appears not only to extract the oxygen but also to combine with the reduced metal. In contact with graphite or nongraphitic carbon, it combines with the carbon, forming a carbide which is soluble in the melt, leaving the carbon surface exposed to further attack.

Thus the key problem in melting of titanium and similar materials is contamination. Efforts at melting and casting of such material emphasize this, since all refractories contaminate molten titanium and this embrittles the resulting metal. Likewise titanium in a highly heated or molten state, also absorbs and is contaminated and embrittled by most gases, including those present in the atmosphere, such as oxygen, nitrogen, hydrogen, etc. It is inert, however, with respect to the noble gases, such as argon, helium, etc.

To overcome this contamination problem, the above said copending application disclosed an arc-melting type skull furnace wherein the high melting point metal which is desired to be melted is charged into a crucible, and the central portion of this charge is then are melted to form a molten pool, which is in turn maintained separated from the walls of the crucible by the skull of unmelted charge, said skull being prevented from melting by appropriate control of the rate at which heat is dissipated therethrough and through the crucible wall. To elfect the aforesaid melting under substantially contamination-free conditions, the crucible and arc-melting equipment are disposed within a housing sealed against outer atmosphere and continuously supplied during the melting operation with an atmosphere of an inert gas such as argon. Such a skull furnace substantially eliminates contamination of the titanium or other metal melted, which would inevitably result and prove harmful to the melt if the same were permitted to contact the crucible walls. This arc-melting type skull furnace has proven highly satisfactory in accomplishing the sought-after results.

Continued work in the development of skull furnaces for the melting of titanium and other similar metals has resulted in the development of a radiation type skull furnace. Heat is supplied to this latter type skull furnace through heating resistors preferably made of graphite and of the type generally disclosed in U. S. Patent Nos. 2,472,612 and 2,472,613 to Poland. In such type furnaces a plurality of resistor bars are connected in series and suspended within the furnace chamber over and in spaced relation to the center of the charge which is to be melted. These resistors are then electrically heated and radiate heat energy which in turn melts the charge. By suitably insulating the furnace walls surrounding the charge and by properly controlling the heat output from the resistor bars it has been found possible to control the rate of heat dissipation through the skull and the furnace walls, thereby permitting the central portion of the charge to be melted while that portion of the charge in contact with the furnace walls remains in the unmelted condition thus forming the skull. As in the arc-melting type skull furnace, the melt can then be cast from the furnace leaving the skull intact and in position to receive another charge.

In such radiation type skull furnaces the roof and walls of the furnace have been formed of graphite and carbon respectively. As the central portion of the titanium charge begins to melt, it has been observed that titanium will evaporate from the molten surface of the charge. As the titanium vapor travels upwardly in the furnace and strikes the carbonaceous resistors, and the graphite roof and carbon walls of the furnace, it is obvious that it will become contaminated and if permitted to return to the molten bath, will in turn contaminate the titanium melt. Furthermore, even if return to the melt is prevented, commingling of this titanium vapor with the carbonaceous structure of the furnace, if it is permitted to continue for a considerable time, will cause severe and irreparable damage to the furnace walls themselves.

These and other difficulties and problems have been overcome by the present invention, which provides an improved apparatus for preventing the harmful eifects of titanium evaporation and presents a radiation type skull furnace which produces a contamination-free titanium melt.

In accordance with the basic principles of the invention a vapor interception roof structure is interposed between the heating resistors and the molten surface of the charge, whereby titanium vapor rising from the melt will be intercepted by this roof before it reaches the resistors or the roof and walls of the furnace. This roof structure is constructed and arranged in relation to a gutter, which is also provided, so that the titanium vapor after being intercepted by the roof will subsequently drain into the gutter and will not return to the melt. In one embodiment of the invention the roof itself is composed of a non-contaminating material such as molybdenum or the like and in this embodiment the necessity for the gutter is of course eliminated, since the titanium vapor is not contaminated on contact with such a roof and may safely return to the melt itself.

Moreover the present invention takes advantage of the continuous sweep of argon gas, designed primarily to remove hydrogen from the furnace, by arranging the path of flow of such gas in such a direction as to aid in the suppression of the titanium vapor from the melt.

Further objects, features and advantages of the invention hereof will appear from the detailed description given below, taken in connection with the accompanying drawings which form a part of this specification and illustrate by way of example, preferred embodiments of the invention.

In the drawings:

Figure 1 is a cross section view of a radiation skull furnace showing one type of interposed roof and cooperating gutter structure;

Figure 2 is a longitudinal section view of the radiation skull furnace of Fig. 1;

Figure 3 is a schematic cross sectional showing of a modified type of roof and gutter structure in a radiation skull furnace;

Figure 4 is a schematic longitudinal sectional view of another modification of the invention showing a radiation skull furnace having its resistors tilted so as to permit drainage of condensate thereupon into a gutter;

Figure 5 is a schematic cross sectional view of an additional modification showing an interposed roof structure of the non-contaminating type in a radiation skull furnace;

Figure 6 is a schematic cross section view of a further modification, showing a radiation skull type furnace having its heating resistors slanted so as to permit drainage of condensate therefrom into a gutter.

Referring now in more detail to the drawings and in particular to Figs. 1 and 2 thereof, a radiation type skull furnace is shown. This furnace it comprises a lower metallic casing 11 and a top metallic cover plate 12, with the latter being removably secured to the former so as to form an integral air-tight structure. Located within the casing 11 is a furnace chamber 30. This fur nace chamber has a hearth formed of massive blocks of hard carbon 33 which are spaced from the bottom of the casing by means of a layer of refractory, heat insulating fire brick 35. As shown in Fig. 1, massive carbon blocks 36 and 37 form the lower portion of the rear and front walls respectively of the furnace chamber. These blocks extend along the entire length of the furnace chamber and are spaced from the bottom, front and rear walls of the casing 11 by the layer of fire brick 35. These blocks 36 and 37 are provided with notches or gutters 38 and 39 which extend longitudinally of the blocks along the entire length of the furnace chamber 30. The function of these gutters 33 and 3? will hereinafter be described in detail. The upper portions of the front and rear walls of the furnace chamber 30 are formed by massive, interfitted carbon blocks 44, 45 and 46, 47 with the lower blocks 44 and 46 being spaced from the casing 11 by the layer of fire brick 35. As shown the blocks 41, 43, 45 and 47, which form the upper portions of the side, front and rear walls of the furnace chamber, are formed to provide a shelf 48 adjacent their tops upon which shelf rests a graphite plate 49 which latter comprises the roof of the furnace chamber. Upon this roof 49 rests a body of refractory heat insulating material 50, preferably lamp black. This body of lampblack is further distributed so as to fill up the space between the hard carbon blocks 4%, 41, 42, 43, 45, 47 and the metallic casing 11. This body of lampblack 5t) together with the layer of firebrick 35 provides a continuous insulating layer completely enveloping the roof, walls and hearth of the furnace chamber 30.

As shown, the furnace is provided with a resistor heating grid 60 comprising a plurality of parallel, elongated resistor bars 61 of heat refractory, electrically conductive material, preferably graphite. These bars are disposed in the upper portion of the furnace chamber and extend lengthwise thereof with their ends extending through opening 62 in connector plates 63 made preferably of the same material as the resistor bars. These conductor plates 63 serve to form a continuous electrically conductive circuit with the resistor bars for series flow of current therethrough. The resistor bars at each end of the series are connected to rigid extensions 64, preferably formed of graphite, which extend through openings 65 formed in the adjacent hard carbon block 45 in spaced relation to the walls of said opening so as to be insulated from said block. In alignment with the openings 65, the lower metallic casing 11 and the body of lamp black 55 are formed with openings through which enlarged diameter portions 66 of the resistor extensions 64 lead to the exterior of the furnace, the openings through the lamp black being constituted as shown by the bores of sleeves 6'7. These sleeves, which are formed of heat refractory electric insulating material preferably fused alumina, at their inner ends abut against the hard carbon block 45 and at their outer ends against the inner surface of casing 11. As shown, the space between the walls of each sleeve and cooperating resistor extension is packed with a yieldable layer 68 of heat refractory material such as asbestos. Terminals 69, for electrical cables for energising the resistor grid, are connected to those ends of the extensions which project outside the furnace, thereby providing for series flow of current through the resistor bars.

The resistor grid 60 is suspended from the graphite roof slab 49 by means of vertically disposed hanger rods 7t), preferably formed of graphite. Screw threadedly connected to the lower ends of these rods are saddle plates 71 having portions 72 projecting laterally of the rods and serving as supports for the connector plates 63. The rods 7t? extend through openings 73 in the graphite roof in out-of-contacting relation to the walls of said openings. Surrounding each rod and resting on the upper side of the roof 49 in recesses 76 formed therein, sleeves 74 are disposed having openings 75 extending therethrough in alignment with the adjacent openings 73. The hanger rods 7t? continue through openings 75 in out-ofcontact relation therewith and are provided at their upper ends with nuts 77, preferably made of graphite. These nuts are screw threaded to the rods and as shown rest on heat refractory electric insulating washers 78, which surround the rods and at their lower sides have reduced diameter portions 79, which fit within the openings 75 of the sleeves '74, thereby preventing the washers from shifting transversely to said sleeves.

The furnace itself is mounted for pivotal or tilting movement about a shaft 91 in the direction of arrow G, Fig. 2. Appropriate means (not shown) for imparting this tilting movement to said furnace when it is desired to discharge titanium melt therefrom are also provided. Extending from outside the furnace through cover plate 12, body of lampblack 50, graphite roof 49 and vapor interception roof 92 into communication with the furnace chamber 36 is a charging tube 90. As shown in Fig. 2 a melt discharge spout 100, having a removable fireclay plug 101, is provided in one of the side walls of the furnace. The discharge spout serves a dual purpose as an outlet passage for inert gas. An inert gas inlet tube 93 extends through the cover plate 12, body of lampblack 50 and graphite roof 49 into the furnace.

The means for preventing contamination of the titanium melt will now be described in detail. In the embodiment of the invention shown in Figs. 1 and 2, a vapor interception roof 92 is interposed between the resistor grid 60 and the hearth. This roof 92, preferably formed of graphite, extends the entire length and width of the furnace chamber 35. It is composed of oppositely inclined slab portions 93 and 94 which slant downwardly from approximately the center of the furnace chamber toward the front and rear thereof and end in vertical alignment with the gutters 38, 39 formed in the carbon blocks 36, 37. Longitudinally extending braces 95, 96 are secured in the side walls of the furnace and serve to support the edges of the roof slabs 93, 94 above the gutters 38, 39. The slabs 93, M are secured in abutting fashion at approximately the center of the furnace chamber by means of a longitudinally extending brace 97 similarly secured in the side walls of the furnace.

Additional means for preventing contamination due to the evaporation of titanium is provided by the sweep of inert gas, such as argon, through the furnace chamber. As mentioned above and discussed fully in the copending application of Milton B. Vordahl and Walter L. Finlay, Serial No. 357,704, an inert gas such as argon is delivered to the interior of the furnace chamber to remove deleterious gases therefrom. As shown in Figs. 1 and 2.

in the present invention, an inert gas inlet tube 98 is located so as to deliver inert gas to the furnace chamber at a point above the vapor interception roof 93 while the discharge spout 100 serves as an exit passage for said gas. Argon or similar gas is fed under pressure through the tube 98 and sweeps down along the upper surface of the vapor interception roof in the direction of the arrows A passing thereunder and across the furnace chamber to the exit passage 19%) as indicated by arrows B. It will be noted that this argon sweep path is generally downward in the furnace and is thus in an opposed relation to the upward path of the titanium vapor rising from the melt. Therefore this sweep of argon gas not only serves to remove deleterious gases from the furnace chamber but also acts against the upward how of titanium vapor anud tends to limit or suppress the same.

When it is desired to melt the initial charge of titanium, titanium sponge is fed through the charging tube 953 into the furnace chamber 30. Electric current is supplied to the resistor heating grid, which in turn radiates heat toward the charge. Since the amount of current to the grid may be controlled, the radiation heat output of that grid may similarly be controlled. Since the vapor interception roof 92 is interposed between the resistor grid and the charge, said roof will be heated to a temperature just below that of the resistor grid and will in turn act as a second radiator delivering heat energy to the charge itself. By appropriately regulating this heat output of the grid and therefore the temperature of the vapor interception roof and charge and by properly insulating the walls of the furnace which surround the charge in the manner above described, the rate of heat dissipation through the outer periphery of the charge and through the walls may be controlled. Sufficient current is supplied to the resistor heating grid to melt the center of the charge of titanium sponge as shown at 104 in Fig. 1 while maintaining the outer peripheral portions and bottom of the charge in a solid state or skull of titanium as designated at 162 in Pig. 1.

The melted portion 1% of the charge is then cast from the furnace by tilting said furnace about its shaft 91 so as to permit discharge of the melt through spout 100. The skull 162 of course remains in place in the furnace and the furnace is at this point prepared for further use and will permit subsequent melts with no contact at all between the molten metal and the furnace walls. In each such subsequent melt the titanium s.-:ull is maintained in a solid condition by repetition of the above described controlling of the current input to the resistor heating grid and by maintaining proper insulation of the furnace.

As has been described above, during heating of the charge titanium vapor will rise in the furnace chamber but due to the position of the vapor interception roof, the vapor will strike the roof before it is able to come into contact with any other p, rt of the furnace. As the titanium vapor comes into contact with the under surface of the vapor interception roof it will condense and drain down in the direction of the inclination of the roof slabs 93 and 94 until it reaches the ends of said roof sides whereupon it will drop into the gutters 38 and 39. Thus even though the titanium vapor becomes contaminated upon contact with the graphite interception roof, this d es not prove to be a contamination factor since that vapor is never permitted to return to the charge itself.

During the above described melting of the charge, argon or a similar inert gas is supplied through inlet tube 98 and sweeps through the furnace in the direction of arrows A and B to the exit passage 1% removing all harmful gases which may be present in the furnace chamber. As has been mentioned above the direction of the sweep of argon gas is such as to counteract the tendency of the titanium vapor to rise upwardly from the melt, and therefore acts as an additional preventative against said 6 titanium vapor being able to reach the roof and walls of the furnace.

In the embodiment of the invention shown in Fig. 3, a modified form of roof and gutter structure is disclosed. As shown there, a radiation skull type furnace having a resistor heating grid 121, charging tube 133, pouring spout 132, a furnace chamber 122 with carbon block side walls 123, 124 having gutters 125, 126 formed therein, is provided with a vapor interception roof 127, which slants downwardly from a ledge 128 formed in one side wal of the furnace to a longitudinally extending brace 129 located near the other side wall of the furnace. This roof extends the entire length and width of the furnace chamber 122 and functions in a substantially identical manner to roof 92 which has been described in connection with Figs. 1 and 2 above. An inert gas inlet 130 permits the entry of gas such as argon under pressure into furnace chamber 122. This gas will flow along the top surface of the roof 127 in the direction of the arrows C and continue around brace 129 to the under side of roof 127, across the charge in the direction of arrows D to the gas exit passage 131. Again the sweep of inert gas is substantially downward and opposed to the upward travel of titanium vapor from the melt and thereby tends to inhibit the latter.

In Fig. 4 a further modification of the invention is disclosed wherein the vapor interception roof is eliminated. There a radiation skull type furnace having a charging tube 138, pouring spout 139 and a furnace chamber 141 with carbon block side walls 142, 143 formed with gutters 144 and 145 therein, is provided with a slanting resistor heating grid 146. The resistor bars 147 of this grid slant downwardly as shown from one side of the furnace chamber to the other with both ends thereof being disposed in vertical alignment with the gutters 144 and 145. In this form of the invention, when titanium vapor begins to rise from the melt as it is heated, said vapor will condense on the resistor bars 147 themselves and will then flow downwardly along the bars and transversely across the melt until it reaches the ends of the bars directly above gutter 144, whereupon the now contaminated titanium condensate will drop into gutter 144 and thus not return to the charge itself. An inert gas inlet passage 143 is similarly provided in this modification so as to permit a sweep of inert gas generally downwardly into the furnace chamber and across the melt in the direction of arrows E and F to a gas discharge passage 149.

In Fig. 5 a further modification of the invention is shown wherein a vapor interception roof which is itself composed on non-contaminating material, such as molybdenum or the like, is provided. There a radiation skull type furnace 150 having a resistor heating grid 151, charging tube 164, pouring spout 166, and suitable insulating carbon block walls 152, 153, is provided with a slanted vapor interception roof 154. As shown, this roof is composed of a V-shaped central portion supported above the surface of the melt by longitudinally extending brace 156 and two side portions 157, 158 which rest at one of their ends on longitudinally extending braces 159, 166 and at the other ends on the titanium skull 161 itself. The lower ends 162 and 163 of the V-shaped portion 155 rest directly on the upper sides of portions 157, 158 of the roof structure so that the roof forms with the titanium skull a complete non-contaminating enclosure. It should be noted that in this form of the invention no gutters are provided for the titanium condensate. Rather as the charge is heated the titanium vapor will rise and strike the under surface of the vapor interception roof 154, whereupon it will condense and then fall or gradually travel downwardly along the under side of the roof until it returns to the titanium melt itself. However, return of this condensate will not contaminate the titanium charge since the roof structure is composed of molybdenum or some other similar non-contaminating material.

Fig. 6 discloses a further modification of the invention wherein a radiation skull type furnace 170, having charging tube 180, pouring spout 179, and a furnace chamber 171 with carbon block side walls 172, 173 formed with gutters 174, 175, is provided with two separate resistor heating grids 176, 177. As shown these grids are supported one at each side of the furnace chamber 171 in vertical alignment with the gutters 174, 175 but are tilted so that their radiant heat will be effectively delivered in the direction of the titanium charge 178. In this embodiment of the invention as the titanium charge 178 is heated, titanium vapor will rise and come in contact with the resistor heating grids 176, 177 whereupon it will become contaminated. However, due to the location of these resistor heating grids directly above the gutters 174, 175, the resulting titanium condensate will drain directly into said gutters and will not return to the melt, thereby avoiding contamination of the latter.

Although certain particular embodiments of the invention are herein disclosed for purposes of explanation, various further modifications thereof, after study of this specification, will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. A metallurgical furnace for melting and casting highly refractory, reactive metals in such manner as to prevent harmful contamination thereof comprising a substantially gas-tight housing, a furnace chamber having a hearth disposed in said housing, insulation means surrounding said furnace chamber and positioned between said chamber and said housing, electrical resistance heating elements disposed in said chamber and positioned so as to radiate heat toward the hearth thereof and melt vapor interception means provided in said furnace chamber.

2. A radiation type skull furnace comprising a furnace chamber having a hearth adapted to hold a mass of highly refractory reactive metal in the molten state, a plurality of electrical resistance heating elements disposed in said chamber and positioned so as to radiate heat toward said hearth in combination with means provided in said furnace chamber and positioned relative to said heating elements and said hearth in such manner as to prevent contamination of the molten mass due to vapor rising therefrom, becoming contaminated and returning thereto.

3. A metallurgical furnace for melting and casting highly refractory, reactive metals in such manner as to prevent harmful contamination thereof comprising a substantially gas-tight housing, a furnace chamber having a hearth disposed in said housing, insulation means surrounding said furnace chamber and positioned between said chamber and said housing, electrical resistance heating elements disposed in said chamber and positioned so as to radiate heat toward the hearth thereof, a vapor interception roof structure interposed between the heating elements and the hearth, and gutter means provided at the sides of the furnace chamber and positioned below said vapor interception roof.

4. A metallurgical furnace for melting and casting highly refractory, reactive metals in such manner as to prevent harmful contamination thereof comprising a substantially gas-tight housing, a furnace chamber having a hearth disposed in said housing, insulation means surrounding said furnace chamber and positioned between said chamber and said housing, electrical resistance heating elements disposed in said chamber and positioned so as to radiate heat toward the hearth thereof, a vapor interception roof structure interposed between the heating elements and the hearth, said vapor interception roof comprising two oppositely inclined slab portions which are supported over the center of the hearth and slant downwardly toward the sides of the furnace chamber and gutter means formed in the side walls of said furnace chamber and positioned vertically below the ends of said vapor interception roof.

5. A metallurgical furnace for melting and casting highly refractory, reactive metals in such manner as to prevent harmful contamination thereof comprising a substantially gas-tight housing, a furnace chamber having a hearth disposed in said housing, insulation means surrounding said furnace chamber and positioned between said chamber and said housing, electrical resistance heating elements disposed in said chamber and positioned so as to radiate heat toward the hearth thereof, a vapor interception roof structure interposed between the heating elements and the hearh and slanting continuously downward from one side of the furnace chamber to the other, and gutter means provided at the side of said chamber and positioned beneath the lowermost point of said roof whereby melt vapor rising in the chamber will condense against the underside of said roof and drain downwardly therealong finally falling into the gutter means.

6. A metallurgical furnace for melting and casting highly refractory, reactive metals in such manner as to prevent harmful contamination thereof comprising a substantially gas-tight housing, a furnace chamber having a hearth disposed in said housing, insulation means surrounding said furnace chamber and positioned between said chamber and said housing, electrical resistance heating elements disposed in said chamber and positioned so as to radiate heat toward the hearth thereof and a vapor interception roof interposed between the heating resistors and the hearth, said roof being formed of non-contaminating material.

7. A metallurgical furnace for melting and casting highly refractory, reactive metals in such manner as to prevent harmful contamination thereof comprising a substantially gas-tight housing, a furnace chamber having a hearth disposed in said housing, insulation means surrounding said furnace chamber and positioned between said chamer and said housing, electrical resistance heating elements inclined downwardly across said chamber from one side thereof to the other, and gutter means provided at the sides of said furnace chamber and positioned beneath said heating elements.

8. A metallurgical furnace for melting and casting highly refractory, reactive metals in such manner as to prevent harmful contamination thereof comprising a substantially gas-tight housing, a furnace chamber having a hearth disposed in said housing, insulation means surrounding said furnace chamber and positioned between said chamber and said housing, electrical resistance heating elements disposed in said chamber extending along the sides thereof and positioned so as to radiate heat toward the hearth thereof, said heating elements and gutter means extending along the sides of said furnace chamber and positioned beneath said heating elements.

9. In a radiation type skull furnace of the kind comprising a substantially gas-tight housing, a furnace chamber having a hearth adapted to hold highly refractory, reactive metals in molten condition disposed in said housing, insulation means positioned between said chamber and said housing, and electrical resistance heating elements positioned in said chamber so as to radiate heat toward the highly refractory metal contained therein, the combination which comprises a vapor interception roof structure interposed between said heating elements and said hearth.

10. In a radiation type skull furnace of the kind comprising a substantially gas-tight housing, a furnace chamber having a hearth adapted to hold highly refractory, reactive metals in molten condition disposed in said housing, insulation means positioned between said chamber and said housing, and electrical resistance heating elements positioned in said chamber so as to radiate heat toward the highly refractory metal contained therein, the combination which comprises a vapor interception roof structure interposed between said heating elements and said hearth and cooperating gutter means located at the sides of the furnace chamber and positioned beneath said roof structure.

11. In a radiation type skull furnace of the kind comprising a furnace chamber having a hearth adapted to hold a molten mass of highly refractory reactive metal, electrical resistance heating elements positioned in said chamber so as to radiate heat toward said hearth and thereby generate said molten mass, the improvement which comprises means provided in said furnace chamber and positioned between said heating elements and said hearth to prevent contamination of the molten mass due to vapor rising therefrom, becoming contaminated and returning thereto.

12. In a radiation type skull furnace of the kind comprising a furnace chamber having a hearth adapted to hold a molten mass of highly refractory reactive metal, electrical resistance heating elements positioned in said chamber so as to radiate heat toward said hearth and thereby generate said molten mass, the improvement which comprises a vapor interception roof structure interposed between said heating elements and said hearth and cooperating gutter means positioned beneath said roof structure whereby vapor rising from the melt will strike the roof, condense and drain into said gutter means.

13. In a radiation type skull furnace of the kind comprising a furnace chamber having a hearth adapted to hold a molten mass of highly refractory reactive metal, electrical resistance heating elements positioned in said chamber so as to radiate heat toward said hearth and thereby generate said molten mass, the improvement which comprises a vapor interception roof formed of noncontaminating material positioned between said heating elements and said hearth so as to prevent contamination of the molten mass due to vapor rising therefrom, becoming contaminated and returning thereto.

14. A radiation type skull furnace of the kind comprising a furnace chamber having a hearth adapted to hold a molten mass of highly refractory reactive metal, electrical resistance heating elements extending longitudinally along the sides of said chamber and positioned to radiate heat toward said hearth and thereby generate said molten 10 mass, and cooperating gutter means positioned beneath said heating elements, whereby vapor rising from the melt and condensing upon the heating elements will fall directly into the gutter means without returning to the melt.

15. A radiation type skull furnace of the kind comprising a furnace chamber having a hearth adapted to hold a molten mass of highly refractory reactive metal, electrical resistance heating elements slanting downwardly across said chamber and positioned to radiate heat toward said hearth and thereby generate said molten mass, and cooperating gutter means provided at the sides of said furnace chamber beneath the ends of said heating elements whereby vapor rising from the melt and condensing upon the heating elements will drain downwardly along said heating elements and fall into said cooperating gutter menas.

16. A radiation type skull furnace of the kind comprising a furnace chamber having a hearth adapted to hold a molten mass of highly refractory reactive metal, electrical resistance heating elements positioned in said chamber so as to radiate heat toward said hearth and thereby generate said molten mass, means provided in said furnace chamber and positioned between said heating elements and said hearth to prevent contamination of the molten mass due to vapor rising therefrom, becoming contaminated and returning thereto, and inert gas entry and exit means positioned in said chamber so as to permit a continuous sweep of inert gas through said chamber with the path of said gas being generally downwardly.

References Cited in the file of this patent UNITED STATES PATENTS 1,904,664 Neuhauss Apr. 18, 1933 2,081,990 Eberwein June 1, 1937 2,252,052 Van Embden Aug. 12, 1941 2,472,612 Poland June 7, 1949 2,472,613 Poland June 7, 1949 2,541,764 Herres et a1. Feb. 13, 1951 2,640,860 Herres June 2, 1953 2,651,668 Southern Sept. 8, 1953 2,680,144 Wilkins et a1. June 1, 1954 

2. A RADIATION TYPE SKULL FURNACE COMPRISING A FURNACE CHAMBER HAVING A HEARTH ADAPTED TO HOLD A MASS OF HIGHLY REFRACTORY REACTIVE METAL IN THE MOLTEN STATE, A PLURALITY OF ELCETRICAL RESISTANCE HEATING ELEMENTS DISPOSED IN SAID CHAMBER AND POSITIONED SO AS TO RADIATE HEAT TOWARD SAID HEARTH IN COMBINATION WITH MEANS PROVIDED IN SAID FURNACE CHAMBER AND POSITIONED RELATIVE TO SAID HEATING ELEMENTS AND SAID HEARTH IN SUCH MANNER AS TO PREVENT 